Slang. something unpleasant that is unexpected or shocking (often used in combination with the first letter of an offensive or unmentionable word, as in f-bomb; s-bomb; n-bomb): He's always dropping the f-bomb.

bomb

n.

1580s, from French bombe, from Italian bomba, probably from Latin bombus "a deep, hollow noise; a buzzing or booming sound," from Greek bombos "deep and hollow sound," echoic. Originally of mortar shells, etc.; modern sense of "explosive device placed by hand or dropped from airplane" is 1909. Meaning "old car" is from 1953. Meaning "success" is from 1954 (late 1990s slang the bomb "the best" is probably a fresh formation); opposite sense of "a failure" is from 1963. The bomb "atomic bomb" is from 1945.